Elastic wave vibrator



1963 H. w. KOMPANE'K 3,101,421-

ELASTIC WAVE VIBRATOR Filed July 6, 1959 2 Sheets-Sheet 1 F l G. 2

o o o o 81 O o 80 82 Q83 0 o O o O o O o o I INVENTOR...

F I G 7 HARRY w. KOMPANEK ATTORNEY Aug. 20, 1963 H. w. KOMPANEK ELASTIC WAVE VIBRATOR Filed July 6, 1959 2 Sheets-Sheet 2 V l 24 2s 2s 3 v I i 22 l 0 4| I 1 L a-fl 7 c 75- z /a L J v [J 70.4 0- TOB N 70.2

\ INVENTOR.

HARRY W. KOMPANEK ATTORNEY Harry Kcmpauck', Santa Barbara, Acoustica Associates, hie, Mineola, N.Y., a corporaoration at frequencies below 9 or kc./sec.

3,101,421? ELASTIC WAVE VllERATQR Calih, assignor to tion of New Yuri: a

1 Filed .l'uly 6, i959, Scr. No. 825,143 7 28 Claims. (Cl. singer This invention relates in general to elastic wave vibrators, and more particularly to electromechanical transducerswhich are especially suit-able for .low frequency operation and methods of manufacturing the same.

Among the most widely used forms of electromeohani cal transducers is the form in which the physical size of the transduceris related to the wavelength therein of elastic waves at the operating frequency (e.g., they are resonant vibrators). Commonamong embodiments of this form is the half-wave longitudijnal vibrator, which is one or more half wavelengths long with respect to such wavelength. Due to the relatively high speed of elastic waves in materials commonly used in such transducers.

brators made of these materials become prohibitively bulky, heavy and costly when designed for use at lower frequencies, such as the lower audible firequencies. Thus,

heretofore half-wave transducers have been commonly found in sizes intended for use at kc./sec., 40 kc./sec., and higher, but rarely are they found designed for op- It is an (piezoelectric, electrostrictive, for example), half-wave longitudinal and other forms of elecm omechanical vi-.

objector the present invention to providev electromechanical transducers which are capable of being operated as resonant vibrators at lower frequencies with little or no increase in physical size. Another object is to provide methods and means to reduce by apprordmately half or more the frequency at which a given transducer can be, operated as a resonant vibrator.

Electromechanical transducers made of certain electrostrictive'mateiials, such as barium titanate and'lead zirconiumtitanate, are advantageously prepolarized by the application of uni-directional potential to them. The voltage required to achieve a useful degree of prepolariza;

'tion increases, for a given material, with the thickness of the body of the material across whichthe voltage is applied. This places a limitation upon the thickness of material across which prepolarizing voltagecan be applied, for eventually the voltage required is so high 7 that voltagebreakdown is an expectedpossibility. The

methods and structures of the invention which provide the feature of reduced resonance frequency for a given piece of transducer material also make it possible usefully to polarize a large body of transducer material in sections at, lower voltage than would be possible in polarizingthe same body as a unit. It. is accordingly an other object of the invention toprovide methods and means for achieving useful polarization of electrostrictive transducer materials at polarization voltages which are reduced with respect to the voltages normally used heretofore, and with no sacrifice in the degree of resulting polarization. 7

According. to the invention, a bodyof material suitable for use as an electromechanical transducer or vibrator intended for vibration in a given direction is perforated,

4 for example, drilled out, in a direction transverse to the direction of vibration. The body is preferably provided with a plurality of such perforations, which may be scattered indiscriminately, orarrayed throughout the body in a prescribed manner. These perforations have the effect of reducing by as much as half or more the velocity of elastic wave energy through the body in the intended vibrational mode, thereby correspondingly reducing the wavelength of such vibration at a given frequency or or lead zirconium titanate, having length L, thickness T ice - 2 vibration. Thus, for example, a body of lead zirconium titanate, which in the unperforated state has a frequency constant K equal to 1400 kc./-sec./rnm. of thickness, can be vperforated.to an extent that it has a frequency constant'K of 900 kc./sec./mm. of thickness and is still useful as an electromechanical transducer. Similarly, for

barium titanate, K, can be reduced from a value of 2400 lie/mm. to approximately 1 600- kc./rnm. by providing it with perforations according to the invention. It is both or two opposite side surfaces), and electrodes in the shape of bands of electric-ally conductive material .are applied to the stern regions of the piezoelectric material between eachperforation andone or both of the 1 other two side surfaces.

Polarizing voltage is then applied between each pair of adjacent electrodes displaced in the longitudinal direction, at a voltage level sulficient to polarize the sectionof the transducer material from one electrode to the next. voltage is a fraction of the voltage which would be required to achievethe same I polarization of the entire body of piezoelectric material if applied across the entire body, from one end tothe other, the fraction being approximately the reciprocal of the number of sections individually polarized. By polarizing the successive sections of the piezoelectric material in relatively opposite senses, and connecting together the alternate electrodes to one terminal and the intervening electrodes to another terminal, the body can be operated as a unitary electromechanical transducer.

Other and further features of the invention will become apparent from the following description of certain embodiments thereof. This description refers to the accompanying drawing, wherein:

FIG. 1 is an isometric view' of a piezoelectric transducer in the form of a longitudinal vibrator;

FIG. 2 is a cross-section along line @-2 in FIG. 1;

FIG. 3 illustrates electrical connections useful with the embodiment of FIG. 1;

FIG. 4 is another embodiment of the invention;

FIG. 5 is a view partly isometric and partly in section of a third embodiment of the invention;

FIG. 6 is an isometric View of still another embodimerit made of magnetostrictive lamin ations; and FIG. 7 is a side view of another embodiment of the invention. 1.

Referring now to FIGS. 1 and 2, a body 1010f polarizable, piezoelectric material, for example barium .ti-tanate and width W, is intended foroperation as 'a longitudinal vibrator, that is avibrator which executes elongation and contraction in the direction of its length L. The length L is, inthe present example, equal to one-half wavelength in the body 10 of vibrations therein at the opera-ting frequency in said direction. A plurality of perforations ll, 12, 13, l4, and 15 pass through the body 10 transversely to the length dimension L, from one of the narrower side surfaces 16 to the other 17. These perforations are round being made by drilling, for example, but other shapes may be used if desired. The'diameters of the perforations shown in FIG. 1 are equal approximately to half the thickness T of the body 10. An individual electrical conductor in the shape of a band 21, 22, 23, 2.4, 25, 26, 2'7, 28, 29, 30 surrounds each stern region of the body 10 between each perforation 11, 12,

.3,ldl,t2l Patented Aug. 20, 1963 are representative of all such stem regions. The individ'ual electrodes 21 :andZZ surrounding these two stem regions, respectively, are also shown in .FIG. 2 illustrating the structure of all the electrodes 21-30, inclusive. The method of polarizing the embodiment of FIGS. 1

and 2, and themode of using it, are illustrated with the aid of FIG. 3, which shows, diagrammatically, the transducer body 10,- perforations 11-15, inclusive, and electrodes 21- 30, inclusive.

I a Polarization The strength .of a D.C; 'fieldrequired for polarization oft-barium-ititanate ceramic is about 12,000 volts per centimeter of thickness of this material between the polarizing electrodes. In'pr'actice higher voltages are used. Thus, :for barium titana-te it is usual to polarize at about 60,000 volts per inch of thickness while for lead zirconium titanateit is usual to use 120,000 volts per inch of thickness. Assuming that the length L of the body in FIG. 1 is six inches, it would require in excess of 700,000 volts at this rate topola-rize lead zirconium titanate through electrodes 38.1 and 39.1 aflixed to the ends 38 and 39 'of the body. The perforations 1110 15, inclusive, however, divide the body 10 into six sections 10.1 to 10.6, inclusive, each of which is approximately one inch long. By

applying 120,000 volts between-eachpair of adjacent electrodes (in the longitudinal direction .L), such as between electrodes 21 and 23, for exam-ple, the section (in the :presentexample section 10.2) between them can be polarized. as effectively as if it'were separated from the i titanate six-and-one-half inches'long, we have a longian operating frequency of about 8-9 kc./sec. As was rest of thebody 10. Preferably this-voltage is applied between both electrodes 21 and 22 at one perforation, 11 and both electrodes 23 and '24 at the next perforation 12. As a convenience for both polarizing'the body 10, and subsequently'for using it as a transducer, the alternate pairs of electrodes 21, 22; 25, 26; and 29, 30 are connected togetherinparallel to one terminal 41, and the intervening electrodes 23, 24; and 27, 28 are connected together in parallel to another terminal 42. The application of approximately 120,000 volts polarizing po- -tential .across these terminalsdl and 42 polarizes the sections 10.2, 10.3, 10.4 and 10.5 between theelectrodes '21, ZZ'and 23, 2 4; 23, 24 and 25, 26; 25, 26 and 27, 28; and 27, 28::and' 20,30, respectively, in alternatelyopposite sense, as indicated by the and signs in FIG. 3.

'If desired electrodes 38.1. and 39.1 may be afiixed to the end surfaces 38 and 39, respectively, and these may be connected to the terminal 42. of the intervening electrodes 23, 24- and27, 28, to polarize the end sections 10.1 and 10.6, in the sense shownoneach in FIG. 3. As the numberofperforations isincreased, however, the utility of the end-electrodes 38.1 and 39.1 decreases. In an embodiment of the invention according to FIGS. 1 and 2 employing twenty perforations in a body of lead zirconium titanate which was siX-and-one-half inches long, so that each section of transducer material between successive electrode pa-irs'was approximately one-third of an inch longypolarization using the circuit of 3 was carried out with 40,000 volts applied across the terminals 41 and 42, and'the end electrodes 3-8.1 and 39.1 were omitted.

Operation as a Transducer The circuit ofFIG. 3 may be used without change to operate embodiments according to FIG. 1 as a transducer simply by connecting the terminals 41 and 42 to a load Y I bodiment of FIG. 1. In FIG. 4, a cylindrical piezoelec- FIG.

ducer is also reduced.

tudinal vibrator which is one-half wavelength long at mentioned above, the frequency constant, K of this material is about 1400 kc./sec./mm. thickness.- As'the thickness increases, the resonance frequency is reduced. The resonance frequency is found by dividing the length L of the body 10 into the frequency constant K for a Thus if In the specific example mentioned above, having twenty perforations in the form of drilled holes arrayed as in 1, K was reduced to approximately 900 kc./sec./mm. In this embodiment, then, the resonance frequency of the bar 10 of length L became %e g- -5.45 lac/sec.

It has been found that the resonance frequency of .a given bar is reduced in proportion to the amount of material which is removed irom the body 10 by the transversely directed apertures (11-15, inclusive,.in FIG. 1), and that at the same time the Q of the resulting trans- Thelimit to the-amount of material that can 'be removed will be determined by the designer, taking into account for example the stiffness of the load into which the transducer is intended to work; as the Q :of the transducer becomes smaller, the stiffness of the load begins to govern its effective Q. The

or more, for many intended uses.

If barium ti-tanate .is used as the transducer material in frequency constant of a given body can be reduced by half place of lead zirconium titanate, the same principles are applicable; .only the numerical values are changed. For

example, polarizing voltages for barium titanate are abouthalf those for lead zirconium titanate. For barium titanate, K =2400 kc./sec./mm. (approximately). of barium titanate six and one-half-inches long and hav- .ing twenty perforations through it according to FIG. 1

' may be made still lower, or both.

FIGS. 4, 5, 6', and 7 showother embodiments of the invention in which the velocity of elastic waves in the transducer body is reduced by perforations transverse to the direction of vibration; these embodimentsdo not incorporate the low voltage polarization feature of the emtric body 50, intended to vibrate axially as indicated by the double-headed arrow 51, has elcctrodes'52 and 53 at its ends connected to terminals54 and 55, respectively.

. A perforation '56 is provided this body, directed dia or a driver in any known manner. The body 10 vibrates as a unit of which the reasonant frequency is determined by its length'L, notwithstanding that it was polarized in sections and is driven or used as a receiver in similar 5 sections.

Velocity Control V I 7 Assuming that the'body 10 in 'FIG. 1 is lead zirconium metrically through the body, so that it is transverse to the direction of vibration. Additional perforations 56.1 may be provided if desired according to the principles set forth above. While these will betransverse to the'direction of vibration, they need not be parallel to each other.

FIG. 5 showsa disk-shaped cylindrical body 60, intended for radial vibration as indicated by the arrows 61. Axially directed perforations 62 are provided in this body, so thatthey are transverse to the direction of vibration. This body is shown as piezoelectric, but it may be magnetostrictive, if desired. The manner of driving it is not illustrated, since'those skilled in the art know how to drive such bodies in a radial vibration mode; The perforations 62 may be arrayed equidistant from the center of A bar f'the long dimension L. .Perforatioris'Yl, 72, 73-, '74 pass through the bar transversely to the longitudinal diperforations in FIG. 1. The bar maybe supp lied with a suit-able coil 75 for use as a transducer and for polarizing purposes, in any well-known manner.

FIG. 7 illustrates a longitudinal vibrator 80, of length L, in which numerous perforations 8'1, 82, 83, etc. all passing through it transversely to the direction of vibration, are. scattered indiscriminately over the surfaces of the bar through which they pass. As is indicatedin FIG.

v 7, the perforatious'can be smaller,} relative to the width "or thickness of the bar, than those shown in FIG. 1.

The number of theseperforationscan, however, be made so great that the frequency constant of the body 80 is reduced by half or more of the frequency constant of ltlof FIGHl, for longitudinal vibration in the direction mension,as"in FIG. 1, and have the same effects as the I the unperforated body. The arrangement according to F1617 enables a precise control of the frequency constant throughout the body sll... i 'i Theembodiments of the invention which have been illustrated and described hereinare but a few illustrations of the invention. Other embodiments and modifications will occur to those skilled in the =ar-t.' No attempt has been made to illustrate all possible embodiments of the ,invention, but rather only to illustrate its principles and the best manner presently known to practice it. Therefore, while certain specific embodiments have been described as illustrative-of theinvention, such other forms I as would occur to one skilled in this art on a reading of the foregoing specification arealso within the spirit and. v, scope of the invention, and it is intended that this invention includes-all modifications andequivalents which fall within the scope of the appendedclaims.

What is'cl'aimed is: A i g i 1. Method of reducing by substantially one-half the velocity of -elastic wave vibrations substantially throughout a solid body intended for resonant vibration in a given direction which comprises perforating the vibrationpropagatiug portion of said body completely through from one side to the opposite side thereof in a direction transverse to the direction of vibration at a vplura-hty of locations throughout a resonant section of said body,

wherebysimultaneously to reduce the'mass and increase the compliance of said body substantially uniformly throughout; I v 2-. Method of polarizing an elongate body of piezoelectric material intended for resonant longitudinal vibration comprising the steps of perforating the-vibrationpropagating portion of said-b ody gcompletely through from one side to theopaposite' side thereof in a direction transverse to-its longitudinal fdimension, whereby simult-aneously to reduce the mass and increase the compliance of said body substantially uniformly throughout at a plurality of locations along said dimension, and polarizopposite to the sense of the contiguous sections and electricallyvconnecting said sections forfcurnulative vibrational and electrical effects. i a

4. Method of polarizing an elongate body of piezoelectric material intended for resonant longitudinal vibration comprising the steps of perforating the vibrationpropagating portion of said body completely through from one side to the opposite sideth'ereof in a direction transverse. to its longitudinal dimension, whereby simultaneously to reduce the mass and increase the compliance of said body substantially uniformly throughout, applying an electrode to at least a portion of each stem region of said body between a perforation and a lateral surface of said body and employing adjacent pairs of said electrodes to polarize each longitudinal section of said body between adjacent pairs of said perforations in the sense opposite to the sense of the contiguous sections.

'5. Method of producing a polarized elongate electromechanical transducer of piezoelectric material intended for resonant longitudinal vibration comprising perforating the vibration-propagating portion of said body completely through from one side to the opposite side thereof in adirection transverse to its longitudinal dimension at a plurality of locations along said dimension, whereby simultaneously to reduce the mass and increase the compliance of said body substantially uniformly throughout,

applying an electrode to at least a portion of each stem region of said body between a perforation and a lateral surface ofsaid body, employing adjacent pairs of said electrodes to polarize each longitudinal sectionof said body between adjacent pairs of said perforations in the sense opposite to the sense of the contiguous sections, connecting alternate ones of'said electrodes to afirst conductor, and connecting the intervening ones of said electrodes to a second conductor.

, 6. Electromechanical vibrator comprising afbody of solid material intended for resonant vibration in a prescribed direction having a plurality of perforations passingcornpletely through said body from one side to the opposite side thereof, each of which is located directly in the path of vibrations in said body and .is' directed transversely to the direction of. vibration at a plurality of locations throughout a resonant sectionof said body,

whereby simultaneously to reduce the mass and increase the compliance of said body substantially uniformly throughout. 1

' 7. Electromechanical vibrator comprising an elongated body of solid material intended for'resonant vibration in the longitudinal direction having a plurality of perforations arrayed throughout a resonant section thereof passa ing completely through it directly in the vibrations path and transversely to the direction of vibration between two opposite side surfaces thereof, whcrebysimult-aneously to reduce the mass and increase the compliance of saidbody substantially uniformly throughout.

8. Electromechanical vibrator comprising an elongated body of solid material intended for resonant vibration in the longitudinal direction and having a plurality of perforations passing completely through it directly in the vibrations path and transversely to the direction of vibration between two opposite side surfaces thereof, said perforations being arrayed indiscriminately on said side surfaces, whereby simultaneously to reduce the rnass'and increase the compliance of said body substantiallyuniformly throughout. 4

, 9.; Electromechanical vibrator comprising an elongated body of solid'rnaterial intended for resonant vibration in the longitudinal direction and having a plurality of perforations passing completely through it directly in the vibrations path .and transversely to the direction of vibration between two opposite side surfaces thereof, said perforation being arrayed along a median line on each of said side surfaces, whereby simultaneously to reduce the mass and increase the compliance of said body substantially uniformly throughout.

10. Electromechanical vibrator comprising an elongated body of solid material intended for resonant vibration in the longitudinal direction and having a rectangular cross section, a plurality of perforations passing completely through said :body directly in thewibra-tions path and'transversely to the direction of vibration between the two opposite narrower side surfaces thereof, the crossgated body of tion in the longitudinal direction and having a rectangular v equidistant from the axis of pletely through saidbody directly in thevibrations path and transversely to the direction of vibration between the two opposite narrower side surfaces thereof, said perforations being arrayed along a median line on each of said side surfaces and having cross-sectional dimensions which are approximately 'half the thickness of said body, where l by simultaneously to reduce the mass and increase the compliance of said body substantially uniformly throughout by amounts which are suificient substantially to reduce by the order'of half the frequency constant of said material.

l2. Electromechanical vibrator comprising an elonsolid material intended for resonant vibracross section, a plurality; of perforations passing completely throughsaid body directly in the vibrations path and transversely to the'direction of vibration between the two opposite narrower side surfaces thereof, said perforations being arrayed substantially uniformly along a median line on each of said side surfaces and having cross-sectional dimensions which are approximately half the thickness of said body, wherebysimultaneously to reduce the mass and increase the compliance of said body substantially uniformly throughout by amounts which are sufficient substantially to reduce by the order of half the frequency constant of said material.

13. Electromechanical vibrator comprising a cylindrical body of solid material intended for resonant vibration in the axial direction and having a plurality of perforations passing diametrically completely through it, said perforations being dimensioned to remove a quantity of said material which simultaneously reduces the mass and increases the compliance of said body by amounts. sufficient substantially to reduce by, the order of half the frequency constant of said material.

14. Electromechanical vibrator comprising a cylindrical body of solid material intended for resonant vibration in the radial direction and having a plurality of perforations passing through it directly in the vibrations path and in the axial direction from one end of said body to the other, said perforations being dimensioned to remove a quantity of said material which simultaneously reduces the mass and increases the compliance. of said body by amounts sufiicient substantially to reduce by the order of half the frequency constant of said material.

sectional dimensions of said perforations being approximately halfthe thickness 'of vsaid body, whereby simultaneously to reduce the mass and increase the compliance 15. Electromechanical vibrator comprising a cylindrioal body of solid material intended for resonant vibration in the radial direction and having a plurality of perforations each of which is axially. directed, said perforation-s being arrayed substantially equidistant from the axis. of said body, said perforations being dimensioned to remove a quantityof said material which simultaneously reduces the mass and increases the compliance of said body by amounts sufiicient substantially to reduce by the order of half the frequency constant of said material.

16. Electromechanical vibrator comprising a cylindrical body of solid material intended for resonant vibration in the radial direction and having a plurality of perforations passing through it directly in the vibrations path and in the axial direction from one end of said body to the -other,. said perforations said body, said perforations being dimensioned to remove a quantity of said material which simultaneously reduces the mass and increases the compliance of Said body by amounts 'sufiicient substanbeing arrayed substantially 8 tially to reduce by the order of half the frequency constant of said material. I

l7. Electromechanical vibrator comprising an elon gated body of piezoelectric material intended for resonant, v

vibration in the longitudinal direction, said body having a plurality of perforations passing completely through it directly in the vibrations path and transversely to' the direction of vibration between two opposite side surfaces thereof, said perforations being arrayed side-by-side in the directionof vibration, said perforations being dimensioned to remove a quantity of said material which simultaneously reduces the mass and increases the compliance of said body by amounts suflicient substantially to reduce by the order of half the frequency constant of said material, the sections of said body between each pair of adjacent perforations being permanently polarized in alternately reversing sense, said sections being electrically connected together for cumulative vibrational and electrical effects.

18. Electromechanical vibrator comprising an eloneach of said narrower side surfaces and having cross-' sectional dimensions which are approximately half the thickness of said body, said perforations being dimen-' sioned to remove a quantity of said material which simultaneously reduces the mass and increases the compliance of said body by amounts sufiicient substantially to reduce by the order of half material, the sections of said body between each pair of adjacent perforations beingpermanently polarized in alternately reversing sense.

l9. Electromechanical vibrator comprising an elongated body of piezoelectric material intended for resonant vibration in the longitudinal direction, said body having a plurality of perforations passing completely through it directly in the vibrations path and transversely to the direction of vibration between a first pair of opposite side surfaces thereof, said perforations being arrayed side-by-si-de in the dircotion of vibration, said perforations being dimensioned to remove a quantity of said material which simultaneously reduces the mass and increases the compliance of said bodyby amounts sufiicient substantially to reduce by the order of half the frequency constant of said material, and a separate bandshaped electrode surrounding at. least one of the two stem regions of said material between each of said perforations and the remaining pair of side surfaces of said body.

20. Electromechanical vibrator comprising an elongated body of piezoelectric material intended for resonant vibration in the longitudinal direction, said body having a plurality of perforations passing completely through it directly in the vibrations path and transversely to the direction-of vibration between a first pair of opposite side surfaces thereof, said perforations being arrayed v side-by-side in the direction of vibration, said perforations being dimensioned to remove a quantity of said body of piezoelectric material intended for resonant vibration in the longitudinal direction, said body having a plurality of perforations passing completely through it directly in the vibrations path and transversely to the directhe frequency constant of said tion of vibration between a first pair of opposite side surfaces thereof, said perforations being arrayed side-by-side in the direction of vibration, said perforations being dimensioned to remove a quantity of said material which simultaneously reduces the mass and increases the compliance of said body by amounts sufficient substantially to reduce by the order of half the frequency constant of said material, the sections of said body between each pair of adjacent perforations being permanently polarized in alternately reversing sense, and a separate band-shaped electrode surrounding at least one of the two stem regions of said material between each of said perforationsand the remaining pair of side surfaces of said body.

22. Vibrator according to claim 21 in which the electrodes at alternate ones of said perforations are electrically connected together, and the electrodes at the intervening ones of said perforations are electrically connected together.

-23. Electromechanical vibrator comprising an elongated body of piezoelectric material intended for resonant vibration in the longitudinal direction and having a rectangular cross section, a plurality of perforations passing completely through said body directly in the vibrations path and transversely to the direction of vibration between the two opposite narrower side surfaces thereof, said perforations being arrayed along a median line on each of said narrower side. surfaces and having cross-sectional dimensions which are approximately half the thickness of said body, whereby simultaneously to reduce the mass and increase the compliance of said body substantially unicfonmly throughout by amounts which are suflicient substantially to reduce by the order of half the frequency constant of said material, the sections of said body between each pair of adjacent perforations being permanently polarized in alternately reversing sense, and a separate band-shaped electrode surrounding each of the stern regions of said material between each of said perforations and the wider side surfaces of said body.

24. Vibrator according to claim 23 in which the electrodes at alternate ones of said perforations are electrically connected together, and the electrodes at the intervening ones of said perforations are electrically connected together.

25. In an elastic wave vibrator comprised of a body of a solid material which in the uniform uninterrupted state has a known [frequency constant with respect to elastic wave vibrations therein parallel to a prescribed direction therethrough, means to reduce the magnitude of the frequency constant of said body with respect to such vibrations therein comprising a plurality of perforations in said body passing completely through said body from one side to the opposite side thereof transverse to said prescribed direction, said perforations being directly in the path of such vibrations.

26. In an elastic Wave vibrator comprised of an elongated body of a solid material which in the uniform uninterrupted state has a known frequency constant with respect to elastic vvave vibrations therein parallel to the length direction thereof, means to reduce the frequency constant of said body with respect to such vibrations comprising a plurality of penforations in said body passing completely through said body from one side to the opposite side theref transverse to said length direction, said perforations being directly in the path of such vibrations.

27. In an elastic wave vibrator comprised of a cylindrical body of a solid material which in the uniform uninterrupted state has a known frequency constant with respect to radially-propagating elastic vvave vibrations therein, means to reduce the frequency constant of said body with respect to such vibrations comprising a plurality of perforations in said body passing completely through said body in the axial direction, said perforations being directly in the path of such vibrations.

28. In an elastic wave vibrator comprised of a cylindrical body of a solid material which in the uniform uninterrupted state has a known frequency constant with respect to axially-propagating elastic wave vibrations therein, means to reduce the frequency constant of said body with respect to such vibrations comprising a plurality of perforations in said body passing diametrically completely through said body, said perforations being directly in the path of such vibrations.

References Cited in the file of this patent UNITED STATES PATENTS 2,540,194 Ellett Feb. 6, 1951 2,841,722 Gravley July 1, 1958 2,870,521 Rudnick Jan. 27, 1959 2,900,536 Palo Aug. 18, 1959 FOREIGN PATENTS 814,123 Great Britain May 27, 1959 

6. ELECTROMECHANICAL VIBRATOR COMPRISING A BODY OF SOLID MATERIAL INTENDED FOR RESONANT VIBRATION IN A PRESCRIBED DIRECTION HAVING A PLURALITY OF PERFORATIONS PASSING COMPLETELY THROUGH SAID BODY FROM ONE SIDE TO THE OPPOSITE SIDE THEREOF, EACH OF WHICH IS LOCATED DIRECTLY IN THE PATH OF VIBRATIONS IN SAID BODY AND IS DIRECTED TRANSVERSELY TO THE DIRECTION VIBRATION AT A PLURALITY OF LOCATIONS THROUGHOUT A RESONANT SECTION OF SAID BODY, WHEREBY SIMULTANEOUSLY TO REDUCE THE MASS AND INCREASE THE COMPLIANCE OF SAID BODY SUBSTANTIALLY UNIFORMLY THROUGHOUT. 